Greater London is an administrative area in England, coterminous with the London region, containing most of the continuous urban area of London. It contains 33 local government districts: the 32 London boroughs, which form a ceremonial county also called Greater London, and the City of London. The Greater London Authority is responsible for strategic local government across the region, and regular local government is the responsibility of the borough councils and the City of London Corporation. Greater London is bordered by the ceremonial counties of Hertfordshire to the north, Essex to the north-east, Kent to the south-east, Surrey to the south, and Berkshire and Buckinghamshire to the west.

Greater London has a land area of 1,572 km² (607 sq mi) and had an estimated population of 9,089,736 in 2024. The ceremonial county of Greater London is only slightly smaller, with an area of 1,569 km² (606 sq mi) and a population of 8,855,333 in 2022. The area is almost entirely urbanised and contains the majority of the Greater London Built-up Area, which extends into Hertfordshire, Essex, Kent, Surrey, and Berkshire and in 2011 had a population of 9,787,426. None of the administrative area, region, or ceremonial county hold city status, but both the City of London and City of Westminster do. The area was historically part of Middlesex, Essex, Surrey, Kent and Hertfordshire.

The River Thames is the defining geographic feature of the area, entering it near Hampton in the west and flowing east before exiting downstream of Dagenham. Several tributaries of the Thames flow through the area, but are now mostly culverted and form part of London's sewerage system. The land immediately north and south of the river is flat, but rises to low hills further away, notably Hampstead Heath, Shooter's Hill, and Sydenham Hill. The area's highest point is Westerham Heights (245 m (804 ft)), part of the North Downs. In the north-east the area contains part of Epping Forest, an ancient woodland.

The City of London has had its own government since the Anglo-Saxon period. The first London-wide directly elected local government was the London County Council, established for the County of London in 1889, which covered the core of the urban area. In 1965 the county was abolished and replaced by Greater London, a two-tier administrative area governed by the Greater London Council, thirty-two London boroughs, and the City of London Corporation. The Greater London Council was abolished in 1986, and its responsibilities largely taken over by the boroughs. The Greater London Authority was formed in 2000.

The term "Greater London" was used before it was established by statute in 1965. It referred to the Metropolitan Police District, the area served by the Metropolitan Water Board, the London Passenger Transport Area, and the area defined by the Registrar General as the "Greater London Conurbation". The term was also used for the Greater London Arterial Road Programme, devised between 1913 and 1916, and the Greater London Planning Region, devised in 1927, which occupied 1,856 square miles (4,810 km²) and included 9 million people.

Although the London County Council (LCC) and County of London were created in 1889, the area did not cover all of London. London's built-up area, postal district, transport network and Metropolitan Police District, extended vastly beyond the boundaries of the new administrative county. Many of the LCC housing projects, including the vast Becontree Estates, were also outside its boundaries. The LCC pressed for an alteration in its boundaries soon after the end of the First World War, noting that within the Metropolitan and City Police Districts there were 122 housing authorities. A Royal Commission on London Government was set up to consider the issue. The LCC proposed a vast new area for Greater London, with a boundary somewhere between the Metropolitan Police District and the home counties. Protests were made at the possibility of including Windsor, Slough and Eton in the authority. The commission made its report in 1923, rejecting the LCC's scheme. Two minority reports favoured change beyond the amalgamation of smaller urban districts, including both smaller borough councils and a central authority for strategic functions. The London Traffic Act 1924 was a result of the commission. Reform of local government in the County of London and its environs was next considered by the Royal Commission on Local Government in Greater London, chaired by Sir Edwin Herbert, which issued the 'Herbert Report' after three years of work in 1960. The commission applied three tests to decide if a community should form part of Greater London: how strong is the area as an independent centre in its own right; how strong are its ties to London; and how strongly is it drawn outwards towards the country rather than inwards towards London.

Greater London was created by the London Government Act 1963, which came into force on 1 April 1965, replacing the administrative counties of Middlesex and London, including the City of London, where the London County Council had limited powers, and absorbing parts of Essex, Hertfordshire, Kent and Surrey. Greater London originally had a two-tier system of local government, with the Greater London Council (GLC) sharing power with the City of London Corporation (governing the small City of London) and the 32 London Borough councils. The GLC was abolished in 1986 by the Local Government Act 1985. Its functions were devolved to the City Corporation and the London Boroughs, with some functions transferred to central government and joint boards. Greater London formed the London region in 1994.

The 1998 London referendum established a public will to recreate an upper tier of government to cover the region. The Greater London Authority, London Assembly and the directly elected Mayor of London were created in 2000 by the Greater London Authority Act 1999. In 2000, the outer boundary of the Metropolitan Police District was re-aligned to the Greater London boundary. The 2000 and 2004 mayoral elections were won by Ken Livingstone, who had been the final leader of the GLC. The 2008 and 2012 elections were won by Boris Johnson. The 2016, 2021 and 2024 elections were won by Sadiq Khan. London was covered by a single Parliamentary constituency in the European Parliament before Brexit.